@aqjune @nunoplopes: See new tests at tests/lean/run/random.lean
We have two actions in `io`. By default, `io` uses the C++
random number generator, but we can force it to use a `std_gen` with
the action `set_rand_gen`.
def rand (lo : nat := std_range.1) (hi : nat := std_range.2) : io nat
def set_rand_gen : std_gen → io unit
Now, `cmp` is just a fixed helper function.
In the future, we will be able to use (more efficient) specialized
versions during code generation by defining simp rules.
closes#1175
The types `string_imp` and `string.iterator_imp` were supposed to be
marked private, but we cannot do it because we need to provide
`string_imp.mk`, `string_imp.cases_on`, `string.iterator_imp.mk` and
`string.iterator_imp.cases_on` in the VM since we use a different
internal representation. Note that marking them as private does not
work since users can still access `string_imp.cases_on` using
meta-programming.
So, we need better support for private declarations.
Missing feature, char literals do not support non ASCII values.
That is, in the current implementation, we cannot write 'α'.
This will be implemented in the future.
The VM native implementation does not behave correctly for huge
strings (i.e., strings with more than 4G characters).
The problem is that the current implementation relies on
```
size_t force_to_size_t(vm_obj const & o, size_t def)
```
We may also have overflow problems in the string.iterator implementation
code. This is not a big deal right now, since I doubt we will try
to process string with more than 2^32 characters.
@Kha the `core_lib` and tests seem to be working correctly, but
we need more tests.
@gebner I used the __builtin_expect trick to optimize the vm_nat module.
Most of the time, we are processing small numbers.
In the following example, the runtime went from 7.27 secs to 6.6 secs
on my machine.
def mk (a : nat) : nat → list nat
| 0 := []
| (nat.succ n) := a :: mk n
def Sum : list nat → nat → nat
| [] r := r
| (n::ns) r := Sum ns (r + n)
def loop : nat → nat → nat
| s 0 := s
| s (nat.succ n) := loop (s + (Sum (mk (n % 2) 1000000) 0)) n
vm_eval timeit "time" $ loop 0 30
